It's a strange one. I definitely had Gsync enabled and global Vsync on (as well as Vsync off ingame). And tested quite a bit with a fresh install of Creators Update, before trying a fresh install of 1607. My experience was pretty much this:
- Creators Update (regardless of Game Mode on/off) and last few sets of drivers - sporadic tearing, and random stuttering/juddering across a range of titles. Reasonably subtle in something like Doom (Vulkan)...but terrible in Rise of The Tomb Raider (especially in DX12) and Rocket League.
- 1607 and any driver more recent than 378.92 - fixed the tearing issues, and less frequent/serious stuttering...but still some random stuttering and frame rate dips.
- 1607 and 378.92 - what I'm using at the moment - absolutely fine.
So yeah, while I'm pleased to have gotten to the bottom of it in my case, it feels like a slightly temporary victory. I'm deferring the update in Windows 10 Pro and hiding the Creators Update itself...but I have little doubt it'll become mandatory in the not-so-distant future. Meanwhile, even the newest 385.12 drivers don't appear to offer a fix for this (although I haven't tried these yet myself).